Signaling of cu based interpolation filter selection

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes processing circuitry that decodes prediction information for a current block in a current coded picture that is part of a coded video sequence. The prediction information indicates a fractional motion vector for the current block. The processing circuitry determines whether one of a block width and a block height of the current block is below a first threshold. The processing circuitry selects one of an integer motion vector, a first interpolation filter, and a second interpolation filter for the current block when the one of the block width and the block height of the current block is determined to be below the first threshold. The processing circuitry reconstructs the current block based on the selected one of the integer motion vector, the first interpolation filter, and the second interpolation filter.

INCORPORATION BY REFERENCE

This present application is a continuation of U.S. application Ser. No.16/815,354, filed Mar. 11, 2020, which claims the benefit of priority toU.S. Provisional Application No. 62/817,507, “SIGNALING OF CU BASEDINTERPOLATION FILTER SELECTION” filed on Mar. 12, 2019, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples. Each sample is labelled with an“S”, its position in the Y dimension (e.g., row index), and its positionin the X dimension (e.g., column index). For example, sample S21 is thesecond sample in the Y dimension (from the top) and the first (from theleft) sample in the X dimension. Similarly, sample S44 is the fourthsample in block (104) in both the Y and X dimensions. As the block is4×4 samples in size, S44 is at the bottom right. Further shown arereference samples that follow a similar numbering scheme. A referencesample is labelled with an R, its Y position (e.g., row index) and Xposition (column index) relative to block (104). In both H.264 andH.265, prediction samples neighbor the block under reconstruction;therefore no negative values need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring areas. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, advanced motion vectorprediction (AMVP) mode and merge mode are described herein.

In AMVP mode, motion information of spatial and temporal neighboringblocks of a current block can be used to predict motion information ofthe current block, while the prediction residue is further coded.Examples of spatial and temporal neighboring candidates are shown inFIG. 1C and FIG. 1D, respectively. A two-candidate motion vectorpredictor list is formed. The first candidate predictor is from thefirst available motion vector of the two blocks A0 (112), A1 (113) atthe bottom-left corner of the current block (111), as shown in FIG. 1C.The second candidate predictor is from the first available motion vectorof the three blocks B0 (114), B1 (115), and B2 (116) above the currentblock (111). If no valid motion vector can be found from the checkedlocations, no candidate will be filled in the list. If two availablecandidates have the same motion information, only one candidate will bekept in the list. If the list is not full, i.e., the list does not havetwo different candidates, a temporal co-located motion vector (afterscaling) from C0 (122) at the bottom-right corner of a co-located block(121) in a reference picture will be used as another candidate, as shownin FIG. 1D. If motion information at C0 (122) location is not available,the center location C1 (123) of the co-located block in the referencepicture will be used instead. In the above derivation, if there arestill not enough motion vector predictor candidates, a zero motionvector will be used to fill up the list. Two flags mvp_l0_flag andmvp_l1_flag are signaled in the bitstream to indicate the AMVP index (0or 1) for MV candidate list L0 and L1, respectively.

In a merge mode for inter-picture prediction, if a merge flag (includinga skip flag) is signaled as TRUE, a merge index is then signaled toindicate which candidate in a merge candidate list will be used toindicate the motion vectors of the current block. At the decoder, themerge candidate list is constructed based on spatial and temporalneighbors of the current block. As shown in FIG. 1C, up to four MVsderived from five spatial neighboring blocks (A0-B2) are added into themerge candidate list. In addition, as shown in FIG. 1D, up to one MVfrom two temporal co-located blocks (C0 and C1) in the reference pictureis added to the list. Additional merge candidates include combinedbi-predictive candidates and zero motion vector candidates. Beforetaking the motion information of a block as a merge candidate,redundancy checks are performed to check whether it is identical to anelement in the current merge candidate list. If it is different fromeach element in the current merge candidate list, it will be added tothe merge candidate list as a merge candidate. MaxMergeCandsNum isdefined as the size of the merge candidate list in terms of candidatenumber. In HEVC, MaxMergeCandsNum is signaled in the bitstream. A skipmode can be considered as a special merge mode with zero residual.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry that decodes prediction information for acurrent block in a current coded picture that is part of a coded videosequence. The prediction information indicates a fractional motionvector for the current block. The processing circuitry determineswhether one of a block width and a block height of the current block isbelow a first threshold. The processing circuitry selects one of aninteger motion vector, a first interpolation filter, and a secondinterpolation filter for the current block when the one of the blockwidth and the block height of the current block is determined to bebelow the first threshold. The first interpolation filter is a blocksize dependent interpolation filter and the second interpolation filteris a block size independent interpolation filter. The processingcircuitry reconstructs the current block based on the selected one ofthe integer motion vector, the first interpolation filter, and thesecond interpolation filter.

In an embodiment, the processing circuitry determines whether both ofthe block width and the block height of the current block are less thanthe first threshold. The processing circuitry selects one of the integermotion vector, the first interpolation filter, and the secondinterpolation filter for the current block when both of the block widthand the block height of the current block are determined to be below thefirst threshold.

In an embodiment, the processing circuitry determines whether the blockwidth of the current block is less than the first threshold and theblock height of the current block is less than a second threshold. Theprocessing circuitry selects one of the integer motion vector, the firstinterpolation filter, and the second interpolation filter for thecurrent block when the block width of the current block is determined tobe less than the first threshold and the block height of the currentblock is determined to be less than the second threshold.

According to aspects of the disclosure, the processing circuitry selectsone of the integer motion vector, the first interpolation filter, andthe second interpolation filter for the current block based on a pictureresolution of the current picture.

In an embodiment, the processing circuitry selects one of the integermotion vector, the first interpolation filter, and the secondinterpolation filter for the current block based on one of a picturewidth, a picture height, a number of pixels in the current picture, aframe rate, and a fill rate of the current picture.

According to aspects of the disclosure, the processing circuitry selectsone of the integer motion vector, the first interpolation filter, andthe second interpolation filter for the current block based on one ormore control flags included in the prediction information.

In an embodiment, the one or more control flags are signaled in at leastone of a sequence level, a picture level, a tile level, a slice level,and a block level.

According to aspects of the disclosure, the processing circuitry selectsone of the integer motion vector, the first interpolation filter, andthe second interpolation filter for the current block based on a memorybandwidth usage in a pixel area that is being decoded in the currentpicture.

In an embodiment, the processing circuitry selects the secondinterpolation filter for the current block before the memory bandwidthusage reaches a target bandwidth. After the memory bandwidth usagereaches the target bandwidth and the pixel area is still being decoded,the processing circuitry selects one of the integer motion vector andthe first interpolation filter for the current block.

Aspects of the disclosure also provide one or more non-transitorycomputer-readable mediums storing instructions which when executed by acomputer for video decoding cause the computer to perform any one or acombination of the methods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions;

FIG. 1C is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example;

FIG. 1D is a schematic illustration of a co-located block and temporalmerge candidates in one example;

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment;

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment;

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment;

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment;

FIG. 8 shows a current block and a reference block of the current blockin accordance with an embodiment;

FIG. 9 shows a flowchart outlining an exemplary process in accordancewith some embodiments; and

FIG. 10 shows a schematic illustration of a computer system inaccordance with an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4 . Brieflyreferring also to FIG. 4 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6 .

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7 .

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (603), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

In inter-prediction, a reference block of a current block is fetchedfrom a reference picture. In certain codec implementations, loading areference block can be time-consuming and limited by hardwarecapabilities. When an MV of a current block has a sub-pel precision(e.g., a fractional MV), extra pixels may need to be loaded into amemory of the codec to predict the current block. For example, as shownin FIG. 8 , to predict an 8×8 luma current block (802) in a currentpicture (801) with an 8-tap interpolation filter, a 15×15 referenceblock (804) in a reference picture (803) may need to be loaded into andfetched from the memory. In addition, when bi-prediction mode is appliedand/or the current picture includes multiple small blocks, memorybandwidth used for loading and/or fetching the reference block(s) maybecome even higher.

Aspects of the disclosure include improvement techniques to reduce thememory bandwidth used for loading/fetching reference blocks for smallblocks.

According to aspects of the disclosure, a current block can beconsidered as a “small block” when a block width or a block height ofthe current block is less than a first threshold, when both the blockwidth and the block height are less than the first threshold, or whenthe block width is less than the first threshold and the block height isless than a second threshold.

According to aspects of the disclosure, when a current block isconsidered as a small block and the current block has a fractional MV,the fractional MV can be rounded to an integer MV before being used inthe prediction for the current block. In an embodiment, for eachdirection (e.g., horizontal or vertical), a fractional MV can be roundedto a nearest integer MV along this direction. For example, a fraction MV(4.6, 3.2) is rounded to (5, 3). In another embodiment, for eachdirection, a fractional MV can be rounded towards zero. For example, thefractional MV (4.6, 3.2) is rounded to (4, 3). That is, each directionof the fraction MV (4.6, 3.2) is rounded down to its respective integerpart.

In some embodiments, an original unrounded fractional MV can be storedin an MV buffer, so that it can be used as a spatial or temporal MVpredictor for other blocks with higher precision.

It is noted that, in some embodiments, the above rounding operations areonly applied to certain combinations of block sizes and colorcomponents, such as 4×4 luma blocks, 4×8 luma blocks, 8×4 luma blocks,2×2 chroma blocks, or 4×4 chroma blocks, etc.

According to aspects of the disclosure, when a current block isconsidered as a small block and the current block has a fractional MV, ablock size dependent interpolation filter can be used for predicting thecurrent block. For the block size dependent interpolation filter, thefilter tap can depend on the block size (e.g., the block width or theblock height) such that a filter with shorter taps can be used for smallblocks.

In an embodiment, a block size dependent filter can be determined at aCU level (e.g., block level). For example, all sub-blocks share the samefilter determined at the CU level in a sub-block based mode (e.g., anaffine mode). In another embodiment, the block size dependent filter canbe applied to non-sub-block modes (e.g., not an affine mode).

In an embodiment, a block size dependent filter can be applied to a lumablock when both a block width and a block height of the luma block aresmaller than a threshold. In an example, the threshold can be 8.

In an embodiment, a blocks size dependent filter can be applied to achroma block when both a block width and a block height of the chromablock are smaller than a threshold. In an example, the threshold can be4.

In an embodiment, a horizontal interpolation filter and a verticalinterpolation filter can have different filter taps. In an example, afilter tap of the horizontal interpolation filter can be determined bythe block width, and a filter tap of the vertical interpolation filtercan be determined by the block height.

In an embodiment, a horizontal interpolation filter and a verticalinterpolation filter can have the same filter tap (or length). Thefilter tap can be determined by a smaller one of a block width and ablock height of a current block. For example, for a 4×8 block, thefilter tap can be determined by the block width (4) instead of the blockheight (8).

In an embodiment, a block size dependent interpolation filter can beapplied to only one direction (e.g., the vertical direction). In anexample, the vertical interpolation filter is block size dependent butthe horizontal interpolation filter is not block size dependent, and thefilter tap of the vertical interpolation filter can be determined by theblock height.

In an embodiment, when a block width or a block height is less than athreshold T, an interpolation filter with a length of N1 can be used.Otherwise, an interpolation filter with a length of N2 can be used. Forexample, T=8, N1=4, and N2=8.

In an embodiment, when a block width or a block height is less than afirst threshold T1, a first interpolation filter with a length of N1 canbe used. When the block width or the block height is less than a secondthreshold T2 and greater than the first threshold T1, a secondinterpolation filter with a length of N2 can be used. Otherwise, a thirdinterpolation filter with a length of N3 can be used. For example, T1=4,T2=8, N1=2, N2=4, and N3=8.

In some embodiments, (N+1) interpolation filters (N>2) can be used ateither a vertical direction or a horizontal direction when there are Nblock size thresholds. In an embodiment, there are three block sizethresholds (T1<T2<T3), i.e., N=3. In this case, when a block width or ablock height is less than T1, a first interpolation filter with a lengthof N1 can be used at either the vertical direction or the horizontaldirection. When the block width or the block height is less than T2 andgreater than T1, a second interpolation filter with a length of N2 canbe used. When the block width or the block height is less than T3 andgreater than T2, a third interpolation filter with a length of N3 can beused. Otherwise, a fourth interpolation filter with a length of N4 canbe used.

In an embodiment, a same rule can be applied to interpolation filters ofluma and chroma blocks. Different rules can be applied to theinterpolation filters of the luma and chroma blocks in otherembodiments. In an example, for a chroma block, the horizontal andvertical interpolation filters can use different taps, while thehorizontal and vertical interpolation filters of a luma block can usethe same tap.

This disclosure also presents techniques to select one of an integer MV,a block size dependent interpolation filter, and a block sizeindependent interpolation filter when a current block is considered as asmall block and the current block has a fractional MV. It is noted thata filter tap of the block size independent interpolation filter does notdepend on the block size, such as the interpolation filters used in HEVCor VVC standards.

In an embodiment, the selection of the integer MV, the block sizedependent interpolation filter, or the block size independentinterpolation filter can depend on a picture resolution of the currentpicture.

In an embodiment, the integer MV and/or the block size dependentinterpolation filter is selected for predicting the current block whenat least one of the following conditions is true: (1) a picture width ofthe current picture is greater than or equal to a threshold T_(width);(2) a picture height of the current picture is greater than or equal toa threshold T_(height); (3) a number of pixels in the current picture isgreater than or equal to a threshold T_(area); (4) a frame rate isgreater than or equal to a threshold T_(hz); (5) a fill rate (e.g.,pixels per second) is greater than or equal to a thresholdT_(totalpixel). Otherwise, the block size independent interpolationfilter is selected for predicting the current block.

In an embodiment, the selection of the integer MV, the block sizedependent interpolation filter, or the block size independentinterpolation filter can depend on one or more control flags that areincluded in the prediction information (e.g., in a high level syntax).For example, the one or more control flags may be signaled at a sequencelevel (e.g., Sequence Parameter Set (SPS)), a picture level (e.g.,Picture Parameter Set (PPS)), a tile group header, a tile header, aslice header, or a block level. One of the integer MV, the block sizedependent interpolation filter, and the block size independentinterpolation filter can be applied to the current block according tothe signaled control flag(s). For example, when the one or more controlflags indicates that the block size independent interpolation filter isto be used, the block size independent interpolation is applied to thesmall blocks indicated by the signaling. In another example, when theone or more control flags indicates that the block size dependentinterpolation filter is to be used, the block size dependentinterpolation filter is applied to the small blocks indicated by thesignaling.

In an embodiment, the selection of the integer MV, the block sizedependent interpolation filter, or the block size independentinterpolation filter can depend on memory bandwidth usage, for examplein a pixel area that is being decoded in the current picture. Forexample, a block size independent interpolation filter can first beapplied to the pixel area, and a counter can be used to calculate thememory bandwidth that is consumed by using the block size independentinterpolation filter for motion compensation. Whether to use a blocksize dependent interpolation filter can depend on the counter. When theconsumed memory bandwidth calculated by the counter reaches a targetbandwidth and the decoding process has not been completed in the pixelarea, the block size dependent interpolation filter will be applied tothe rest of the pixel area that is still being decoded. In someembodiments, the counter may be reset to 0 for a new pixel area. Thepixel area may be a coding tree unit (CTU), a CTU row, a tile, a tilegroup, a wave front, and a constant number of pixels, etc. Theinformation of the pixel area may be signaled in the predictioninformation, such as SPS, and PPS, etc.

FIG. 9 shows a flowchart outlining an exemplary process (900) accordingto some embodiments of the disclosure. In various embodiments, theprocess (900) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (900) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(900).

The process (900) may generally start at step (S901), where the process(900) decodes prediction information for a current block in a currentpicture that is a part of a coded video sequence. The predictioninformation indicates a fractional motion vector for the current block.Then the process (900) proceeds to step (S902).

At step (S902), the process (900) determines whether one of a blockwidth and a block height of the current block is below a firstthreshold. When the one of the block width and the block height of thecurrent block is determined to be below the first threshold, the process(900) proceeds to step (S903).

At step (S903), the process (900) selects one of an integer motionvector, a first interpolation filter, and a second interpolation filterfor the current block. The first interpolation filter is a block sizedependent interpolation filter and the second interpolation filter is ablock size independent interpolation filter. Then the process (900)proceeds to step (S904).

At step (S904), the process (900) reconstructs the current block basedon the selected one of the integer motion vector, the firstinterpolation filter, and the second interpolation filter. Afterreconstructing the current block, the process (900) terminates.

In an embodiment, the process (900) determines whether both of the blockwidth and the block height of the current block are less than the firstthreshold. When both of the block width and the block height of thecurrent block are determined to be below the first threshold, theprocess (900) selects one of the integer motion vector, the firstinterpolation filter, and the second interpolation filter for thecurrent block.

In an embodiment, the process (900) determines whether the block widthof the current block is less than the first threshold and the blockheight of the current block is less than a second threshold. When theblock width of the current block is determined to be less than the firstthreshold and the block height of the current block is determined to beless than the second threshold, the process (900) selects one of theinteger motion vector, the first interpolation filter, and the secondinterpolation filter for the current block.

In an embodiment, the process (900) selects one of the integer motionvector, the first interpolation filter, and the second interpolationfilter for the current block based on a picture resolution of thecurrent picture.

In an embodiment, the process (900) selects one of the integer motionvector, the first interpolation filter, and the second interpolationfilter for the current block based on one of a picture width, a pictureheight, a number of pixels in the current picture, a frame rate, and afill rate of the current picture.

In an embodiment, the process (900) selects one of the integer motionvector, the first interpolation filter, and the second interpolationfilter for the current block based on one or more control flags includedin the prediction information. The one or more control flags aresignaled in at least one of a sequence level, a picture level, a tilelevel, a slice level, and a block level.

In an embodiment, the process (900) selects one of the integer motionvector, the first interpolation filter, and the second interpolationfilter for the current block based on a memory bandwidth usage in apixel area that is being decoded in the current picture. Before thememory bandwidth usage reaches a target bandwidth, the process (900)selects the second interpolation filter for the current block. After thememory bandwidth usage reaches the target bandwidth and the pixel areais still being decoded, the process (900) selects one of the integermotion vector and the first interpolation filter for the current block.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 10 shows a computersystem (1000) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 10 for computer system (1000) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1000).

Computer system (1000) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1001), mouse (1002), trackpad (1003), touchscreen (1010), data-glove (not shown), joystick (1005), microphone(1006), scanner (1007), camera (1008).

Computer system (1000) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1010), data-glove (not shown), or joystick (1005), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1009), headphones(not depicted)), visual output devices (such as screens (1010) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted). These visual output devices (such as screens(1010)) can be connected to a system bus (1048) through a graphicsadapter (1050).

Computer system (1000) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1020) with CD/DVD or the like media (1021), thumb-drive (1022),removable hard drive or solid state drive (1023), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1000) can also include a network interface (1054) toone or more communication networks (1055). The one or more communicationnetworks (1055) can for example be wireless, wireline, optical. The oneor more communication networks (1055) can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of the one or more communication networks (1055) includelocal area networks such as Ethernet, wireless LANs, cellular networksto include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (1049) (such as, for example USB ports of thecomputer system (1000)); others are commonly integrated into the core ofthe computer system (1000) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1000) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1040) of thecomputer system (1000).

The core (1040) can include one or more Central Processing Units (CPU)(1041), Graphics Processing Units (GPU) (1042), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1043), hardware accelerators for certain tasks (1044), and so forth.These devices, along with Read-only memory (ROM) (1045), Random-accessmemory (1046), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1047), may be connectedthrough the system bus (1048). In some computer systems, the system bus(1048) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1048),or through a peripheral bus (1049). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1041), GPUs (1042), FPGAs (1043), and accelerators (1044) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1045) or RAM (1046). Transitional data can be also be stored in RAM(1046), whereas permanent data can be stored for example, in theinternal mass storage (1047). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1041), GPU (1042), massstorage (1047), ROM (1045), RAM (1046), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1000), and specifically the core (1040) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1040) that are of non-transitorynature, such as core-internal mass storage (1047) or ROM (1045). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1040). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1040) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1046) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1044)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

Appendix A: Acronyms

-   -   AMVP: Advanced Motion Vector Prediction    -   ASIC: Application-Specific Integrated Circuit    -   BMS: Benchmark Set    -   BS: Boundary Strength    -   BV: Block Vector    -   CANBus: Controller Area Network Bus    -   CD: Compact Disc    -   CPR: Current Picture Referencing    -   CPUs: Central Processing Units    -   CRT: Cathode Ray Tube    -   CTBs: Coding Tree Blocks    -   CTUs: Coding Tree Units    -   CU: Coding Unit    -   DPB: Decoder Picture Buffer    -   DVD: Digital Video Disc    -   FPGA: Field Programmable Gate Areas    -   GOPs: Groups of Pictures    -   GPUs: Graphics Processing Units    -   GSM: Global System for Mobile communications    -   HDR: High Dynamic Range    -   HEVC: High Efficiency Video Coding    -   HRD: Hypothetical Reference Decoder    -   IBC: Intra Block Copy    -   IC: Integrated Circuit    -   JEM: Joint Exploration Model    -   LAN: Local Area Network    -   LCD: Liquid-Crystal Display    -   LIC: Local Illumination Compensation    -   LTE: Long-Term Evolution    -   MR-SAD: Mean-Removed Sum of Absolute Difference    -   MR-SATD: Mean-Removed Sum of Absolute Hadamard-Transformed        Difference    -   MV: Motion Vector    -   OLED: Organic Light-Emitting Diode    -   PBs: Prediction Blocks    -   PCI: Peripheral Component Interconnect    -   PLD: Programmable Logic Device    -   PPS: Picture Parameter Set    -   PUs: Prediction Units    -   RAM: Random Access Memory    -   ROM: Read-Only Memory    -   SCC: Screen Content Coding    -   SDR: Standard Dynamic Range    -   SEI: Supplementary Enhancement Information    -   SMVP: Spatial Motion Vector Predictor    -   SNR: Signal Noise Ratio    -   SPS: Sequence Parameter Set    -   SSD: Solid-state Drive    -   TMVP: Temporal Motion Vector Predictor    -   TUs: Transform Units    -   USB: Universal Serial Bus    -   VUI: Video Usability Information    -   VVC: Versatile Video Coding

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information for a current block in acurrent picture that is a part of a coded video sequence, the predictioninformation indicating a fractional motion vector for the current block;selecting one of an integer motion vector, a first interpolation filter,or a second interpolation filter for the current block including beforea memory bandwidth usage in a pixel area that is being decoded reaches atarget bandwidth, selecting the second interpolation filter having anumber of taps independent of block size, and after the memory bandwidthusage reaches the target bandwidth and the pixel area is still beingdecoded, selecting one of (i) the first interpolation filter having anumber of taps dependent on the block size or (ii) the integer motionvector; and reconstructing the current block based on the selected oneof the integer motion vector, the first interpolation filter, or thesecond interpolation filter.
 2. The method of claim 1, furthercomprising determining whether one of a block width and a block heightof the current block is below a first threshold, wherein the selectingincludes selecting one of the integer motion vector, the firstinterpolation filter, or the second interpolation filter for the currentblock when the one of the block width and the block height of thecurrent block is determined to be below the first threshold.
 3. Themethod of claim 2, wherein the determining includes determining whetherboth of the block width and the block height of the current block areless than the first threshold; and the selecting includes selecting oneof the integer motion vector, the first interpolation filter, or thesecond interpolation filter for the current block when both of the blockwidth and the block height of the current block are determined to bebelow the first threshold.
 4. The method of claim 2, wherein thedetermining includes determining whether the block width of the currentblock is less than the first threshold and the block height of thecurrent block is less than a second threshold; and the selectingincludes selecting one of the integer motion vector, the firstinterpolation filter, or the second interpolation filter for the currentblock when the block width of the current block is determined to be lessthan the first threshold and the block height of the current block isdetermined to be less than the second threshold.
 5. The method of claim1, wherein the selecting is based on a picture resolution of the currentpicture.
 6. The method of claim 1, wherein the selecting is based on oneof a picture width, a picture height, a number of pixels in the currentpicture, a frame rate, and a fill rate of the current picture.
 7. Themethod of claim 1, wherein the selecting is based on one or more controlflags included in the prediction information.
 8. The method of claim 7,wherein the one or more control flags are signaled in at least one of asequence level, a picture level, a tile level, a slice level, and ablock level.
 9. An apparatus for video decoding, comprising processingcircuitry configured to: decode prediction information for a currentblock in a current picture that is a part of a coded video sequence, theprediction information indicating a fractional motion vector for thecurrent block; select one of an integer motion vector, a firstinterpolation filter, or a second interpolation filter for the currentblock including before a memory bandwidth usage in a pixel area that isbeing decoded reaches a target bandwidth, select the secondinterpolation filter having a number of taps independent of block size,and after the memory bandwidth usage reaches the target bandwidth andthe pixel area is still being decoded, select one of (i) the firstinterpolation filter having a number of taps dependent on the block sizeor (ii) the integer motion vector; and reconstruct the current blockbased on the selected one of the integer motion vector, the firstinterpolation filter, or the second interpolation filter.
 10. Theapparatus of claim 9, wherein the processing circuitry is furtherconfigured to: determine whether one of a block width and a block heightof the current block is below a first threshold; and selecting one ofthe integer motion vector, the first interpolation filter, or the secondinterpolation filter for the current block when the one of the blockwidth and the block height of the current block is determined to bebelow the first threshold.
 11. The apparatus of claim 10, wherein theprocessing circuitry is further configured to: determine whether both ofthe block width and the block height of the current block are less thanthe first threshold; and select one of the integer motion vector, thefirst interpolation filter, or the second interpolation filter for thecurrent block when both of the block width and the block height of thecurrent block are determined to be below the first threshold.
 12. Theapparatus of claim 10, wherein the processing circuitry is furtherconfigured to: determine whether the block width of the current block isless than the first threshold and the block height of the current blockis less than a second threshold; and select one of the integer motionvector, the first interpolation filter, or the second interpolationfilter for the current block when the block width of the current blockis determined to be less than the first threshold and the block heightof the current block is determined to be less than the second threshold.13. The apparatus of claim 9, wherein the processing circuitry isfurther configured to: select one of the integer motion vector, thefirst interpolation filter, or the second interpolation filter for thecurrent block based on a picture resolution of the current picture. 14.The apparatus of claim 9, wherein the processing circuitry is furtherconfigured to: select one of the integer motion vector, the firstinterpolation filter, or the second interpolation filter for the currentblock based on one of a picture width, a picture height, a number ofpixels in the current picture, a frame rate, and a fill rate of thecurrent picture.
 15. The apparatus of claim 9, wherein the processingcircuitry is further configured to: select one of the integer motionvector, the first interpolation filter, or the second interpolationfilter for the current block based on one or more control flags includedin the prediction information.
 16. The apparatus of claim 15, whereinthe one or more control flags are signaled in at least one of a sequencelevel, a picture level, a tile level, a slice level, and a block level.17. A non-transitory computer-readable storage medium storing a programexecutable by at least one processor to perform: decoding predictioninformation for a current block in a current picture that is a part of acoded video sequence, the prediction information indicating a fractionalmotion vector for the current block; selecting one of an integer motionvector, a first interpolation filter, or a second interpolation filterfor the current block including before a memory bandwidth usage in apixel area that is being decoded reaches a target bandwidth, selectingthe second interpolation filter having a number of taps independent ofblock size, and after the memory bandwidth usage reaches the targetbandwidth and the pixel area is still being decoded, selecting one of(i) the first interpolation filter having a number of taps dependent onthe block size or (ii) the integer motion vector; and reconstructing thecurrent block based on the selected one of the integer motion vector,the first interpolation filter, and the second interpolation filter.